A die or punch for a press tool

ABSTRACT

A die or punch is provided for a press tool. The die or punch includes a body and a roller assembly having a holder and a roller. The holder is shaped to slidably engage with a complementary cavity in the body to facilitate secure installation of the holder in the body. The holder is able to be removably inserted into the body to present the roller as a forming edge to shape a work piece in a press tool. The roller is able to turn with respect to the holder when shaping a work piece to protect the roller against wear.

FIELD OF INVENTION

This invention relates to a die or punch for use in a press tool. Apreferred form of the invention relates to a die or punch with areplaceable shoulder portion for a power press.

BACKGROUND

Metal presses come in many and varied forms. At one end of the spectrumis the “garage press” which is a simple and low cost fabricatedconstruction designed to be versatile for the many and varied one-offtasks that it might be needed for in an automotive workshop, i.e.removal of bearings from a wheel hub etc. At the other end of thespectrum is the high precision, high speed “minting press” designed tostamp out coinage with extreme accuracy by the millions. Other commonpresses within this spectrum include Press Brakes and power presses.Press Brakes are designed to manufacture long sheet metal componentssuch as storage cabinets and building products like roof guttering etc.Power press is a generic term used for the most common type of pressthat is used to manufacture a myriad of metal components that are ineveryday use, ranging from small automotive components to buildingbracketry, furniture, electrical goods, componentry and an endless listof other everyday widgets.

A Press Brake is typically a machine used to bend relatively thin piecesof sheet metal one simple fold at a time. Because the machine is used tobend thin pieces of sheet metal the forces exerted on the work piece arerelatively small. The machine can be easily changed to varying speedsand stroke heights (the extent to which the punch travels down towardsthe work piece and die). The tools for a Press Brake are standard andcan be fitted or removed quickly. Press Brake tools are typicallyrelatively lightweight and can be lifted by hand. In a Press Brakeoperation, at the bottom of the stroke there is usually only contact onthe work piece at three points; from the punch on the top middle and thetwo shoulders of the die on the bottom.

A power press is used to bend or punch holes in relatively thick piecesof metal. The forces exerted by a power press are much greater thanthose exerted by a typical Press Brake. A power press is set up to veryfine tolerances; for example the tools used in the power press arefitted onto slides to ensure that they are always in the same positionrelative to one another. Power press tools—comprising a die and apunch—are securely fitted to the machine; a process that can easily takean hour or more. The tools are made from solid steel and are very heavy,often requiring special equipment to lift them into position. At thebottom of the power press stroke the work piece is usually completelysandwiched between the punch and the die, i.e. there is no gap anywhere.

In a power press the radius of the shoulders of the tools is normallydetermined by the thickness of the work piece. The cosmetic appearanceof the work piece is, generally speaking, not so important. A powerpress is normally used for repetitive press work—one machine mightperform 10,000 identical operations a day, day in, day out. Powerpresses are not usually used to make one-off bends in sheet metal.

Tools used in power presses are often made from heat treated andhardened specialist tool steels. High carbon steel can be hardened byfirst heating the steel then rapidly cooling the steel. The steel isthen reheated to a lower temperature and allowed to cool slowly. It issometimes just possible to tap a threaded hole into a hardened steeltool. However it is extremely difficult and expensive to do so. It isusually more cost effective to replace a hardened steel tool than to tapa threaded hole into the tool.

It is a problem to constantly repair or maintain the hardest workedareas of a metal forming tool used in a power press. The hardest workedareas of a tool are usually the shoulders. Damage to the shoulders iscaused by the work piece being drawn across the shoulder, or theshoulder being drawn across the work piece. Basically the damage iscaused by the friction between the two faces generating enough heat at amicroscopic level that some of the surface particles melt and then causefurther damage to the surrounding face. Factors that determine theamount of damage sustained by the tool include:

-   -   The properties of the work piece material    -   The pressure exerted between the face of the tool shoulder and        the work piece    -   The speed at which the work piece is drawn over the tool        shoulder or the tool shoulder is drawn over the work piece    -   The amount and quality of lubricant between the faces    -   The quality of the tooling material    -   The surface finish of both the work piece and the tooling        material    -   General cleanliness of the surfaces of the work piece and the        tool shoulder    -   Other minor factors such as room temperature    -   Production rate (the more uses of the tool per hour the more        frequently the tool may need replacing due to damage).

It is an object of a preferred embodiment of the present invention to goat least some way towards addressing the problem of damage to theshoulder or shoulders of the tool. While this object applies to thepreferred embodiment, it should be understood that it is not intended tolimit the scope of the claims. This is because the object of theinvention per se is simply to provide the public with a useful choice.

The term “comprising” and derivatives thereof, e.g. “comprises”, if andwhen used herein in relation to a combination of features should not betaken as excluding the possibility that the combination may have furtherunspecified features. For example, a statement that an arrangement“comprises” certain parts does not mean that it cannot also, optionally,have additional parts.

SUMMARY OF INVENTION

According to one aspect of the invention there is provided a die orpunch for a press tool comprising:

a body; and

a roller assembly having a holder and a roller;

the holder shaped to slidably engage with a complementary cavity in thebody to facilitate secure installation of the holder in the body, theholder being able to be removably inserted into the body to present theroller as a forming edge to shape a work piece in a press tool, theroller being able to turn with respect to the holder when shaping thework piece to protect the roller against wear.

Optionally the roller comprises a cylinder arranged to turn, and whichis replaceable, with respect to the holder.

Optionally the roller is releasably secured to the holder by way of aclip.

Optionally the roller has a groove to facilitate securement by the clip.

Optionally the holder comprises a slot to facilitate securement of theclip.

Optionally the clip is generally in a horseshoe shape.

Optionally ends of the roller are held in end retaining plates and theroller is able to rotate with respect to the plates.

Optionally the holder has at least one channel adapted to enable thepassage of lubricant from an aperture in the holder to the roller.

Optionally there are two channels which run from opposite ends of theholder.

Optionally the holder has at least one fastening groove in a sidethereof adapted to engage with a complementary protrusion in the body tofacilitate secure installation of the holder in the body.

Optionally there are two fastening grooves, each running substantiallythe length of opposite sides of the holder.

Optionally the holder is shaped to retain the roller in place in thepress tool.

Optionally the roller assembly bisects the internal angle of theshoulder of the body of the die or punch to which it is fitted.

Optionally the press tool is a fitted to a power press.

Optionally the press tool is made from hardened steel.

Optionally the roller assembly is retrofitted to the punch or die.

Optionally the holder has a wider portion at or towards the base of theholder when compared to the roller end of the holder.

BRIEF DESCRIPTION OF THE DRAWINGS

Some preferred forms of the invention will now be described by way ofexample and with reference to the accompanying drawings, of which:

FIG. 1 is a schematic side view showing a press tool in 3 dispositionsof use;

FIG. 2 is a schematic side view of parts of the press tool when in use;

FIG. 3 is an isometric view of the press tool in more detail, after thework piece has been formed;

FIG. 4 is an exploded isometric view illustrating a roller assembly;

FIG. 4A is an exploded isometric view illustrating a second embodimentof roller assembly;

FIG. 5 is an isometric view of the roller assembly of FIG. 4 whenassembled;

FIG. 6 is an exploded end view of the roller assembly of FIG. 4;

FIG. 7 is an exploded side view of the roller assembly of FIG. 4;

FIG. 8 is a cross-section end view of the roller assembly whenassembled, at the point where the clip holds the roller in place;

FIG. 9 shows end views of a number of different holder shapes;

FIG. 10A is a schematic side view of the press tool in use, particularlyillustrating one of the roller assemblies;

FIG. 10B is a schematic side view of a press tool in use, particularlyillustrating another embodiment of roller assembly;

FIG. 11 is an isometric view of a solid one piece insert without aroller assembly, prior to installation;

FIG. 12 is an isometric view showing detail of a roller;

FIG. 13 is an isometric exploded view of an alternative roller assembly;

FIG. 14 is an isometric view of the alternative roller assembly whenassembled;

FIG. 15 is a schematic side view of an alternative press tool prior tooperation;

FIG. 16 is a schematic side view of the alternative press tool at aninitial stage of operation;

FIG. 17 is a schematic side view of the alternative press tool at afurther advanced stage of operation; and

FIG. 18 shows a die and punch with a plurality of rollers and holders

DETAILED DESCRIPTION

FIG. 1 shows a power press tool 1 having a die 2 and a punch 3 in threestages of use. The left hand image shows the punch 3 ready to move downon a work piece 4 in the form of a piece of metallic material laid overthe die 2. The centre image shows the punch 3 just after it has firstmade contact with the work piece 4. The right hand image shows the powerpress tool when the punch is fully in the die's cavity 5 and has causedthe work piece 4 to assume the shape of the cavity.

Referring to FIG. 2, the shoulder 6 of the die 2 is exposed tosubstantial wear inducing force via the work piece 4 as the punch 3forces the work piece 4 across it. The work piece may also receive scuffmarks from being forced across the shoulder 6 of the die 2. These scuffmarks require linishing to remove. Linishing involves grinding or beltsanding the affected area to improve the flatness of the surface.Linishing may also include polishing the surface. However, the presstool 1 shown in FIG. 3 has features (not shown in FIGS. 1 and 2) toaddress this.

Referring to FIG. 3, each shoulder of the die 2 has an interferencefitted releasable wear resistant roller assembly 7. The roller assembly7 slides into the shoulder 6 of the die at an angle which bisects theinternal angle of the die, and presents a rolling curved wear edge 8 forcontacting the work piece 4. The angle of the roller assembly 7 withrespect to the shoulder of the die is preferably one which bisects theincluded angle of the shoulder of the die. In this case the includedangle of the shoulder of the die is 90° and the angle of the rollerassembly is about 45°. To facilitate fitting of the roller assembly intothe die, the roller assembly has longitudinal grooves 7 a (see FIGS. 4and 5) formed to engage with complementary protrusions (not shown) inthe main body of the die. In some embodiments the rollers extend to theedge of the die. The rolling edge 8 enables the work piece 4 to rollover it and avoid the type of point loading that would occur if the edgewas static.

Alternatively the roller assembly may be any suitable shape to fit thecomplementary cavity in the punch and/or die 2. FIG. 9 shows differentembodiments of roller assembly 7 that can be used. While FIGS. 4, 4A and5 show roller assemblies 7 with grooves 7 a to engage with complementaryprotrusions it should be appreciated that these are not essential toevery embodiment of roller assembly 7. For example, roller assemblies29-33 of FIG. 9 do not have grooves. It is possible for the rollerassembly to be any suitable shape to engage the complementary cavity inthe punch 3 and/or die 2. A suitable shape is one that has a uniformcross section in a plane from the roller to the base (for example, asshown in FIG. 9) and can be fitted to the punch and/or die by means ofan interference fit. It is possible for roller assembly 7 to haveprotrusions and the punches and/or dies to have complementary groovesfor example. As shown in FIG. 9 some embodiments of roller assemblieshave bases wider than the roller portions. Others (for example 27 and28) have grooves that fit complementary protrusions in the punch 3and/or die 2. Each of the roller assemblies is arranged to form aninterference fit into a complementary cavity in the punch 3 and/or die2. As shown in FIG. 9 the shape of the roller assembly holder may vary.In preferred embodiments the roller assembly holder has as least threedistinct faces that form an interference fit with three distinct sidesof a cavity in the die 2 or punch 3. As shown in FIG. 9, some holdersmay have more than three distinct faces that form the interference fitwith corresponding faces in the punch 3 or die 2.

The rolling edge 8 means that the work piece 4 is no longer scraped overthe shoulder of the die 2. Due to the reduction in friction between theshoulder of the die 2 and the work piece 4 less force is required toform the work piece than when a static shoulder is present on die 2. Theaction of rolling edge 8 also reduces scuffing on the work piece meaningthat the need to linish the work piece to repair shoulder damage issignificantly reduced or eliminated.

The wear resistant roller assembly 7 is shown in more detail at FIGS.4-8. As particularly shown in FIG. 4A, it comprises a holder 9 with anupper edge in the form of a cradle 10. A roller 11 in the form of ametallic bar, which is circular in transverse cross section, sits in thecradle 10. The holder and roller are preferably made from bearingcompatible materials. The materials used may be influenced by theparticular work to be performed and the functionality required. Apreferred combination would be a phosphor bronze holder and a hardenedsteel roller.

In preferred embodiments the rollers are manufactured from hardenedsteel. In these embodiments it may be possible to manufacture theremainder of the punch and/or die from less hard, less expensivematerials that won't necessarily need to be hardened. If the punchand/or die can be manufactured from a less expensive material then thereare potential savings to be made in costs, machining and lead time.

The roller is held in the holder by way of a clip 12. The clip 12 isreleasably secured in a slot 13 of the holder and engages a groove 14 ofthe roller 11. The arrangement is such that the roller 11 can turn whilesitting in the cradle, to reduce frictional wear as the work piece movesacross it under pressure from the punch. The roller 11 may or may nothave a hollow centre. In some embodiments there may be multiple of theclips, all installed the same way in spaced relationship, depending onthe length of the roller 11. FIG. 4A shows an embodiment with two clips,one at each end of the roller. The clips 12 help maintain the roller inposition in the holder 9 and provide means for connecting the roller andholder to prevent the roller moving along its rotational axis withrespect to the holder.

Wear is also addressed by a lubricant system. Referring to FIGS. 4A and5, the holder 9 has a channel 15 at each end. As indicated in FIG. 7,the channels 15 lead to the cradle 10. Lubricant can be pumped into thechannels so it reaches the cradle, provides lubrication to the roller 11and further reduces wear and tear to the roller assembly 7.

Referring to FIG. 12, in some embodiments of the invention the roller 11may have a grooved marker line 11 a at one end, or on some other part ofits surface, so that an operator can easily observe whether it isturning in use, as it should be. If it is not turning, then the operatorcan apply more lubricant via the channels 15 and/or disassemble toinvestigate the cause of the roller ceasing to rotate.

FIG. 10A illustrates contact between the work piece 4 and the die 2 whena roller assembly 7 is in place (some of the features mentioned aboveare omitted, for ease of illustration). As can be seen in FIG. 10A thetool with holder and roller has the same overall dimensions as a toolwithout the holder and roller. No additional plates or fastenings areneeded. The roller extends the length of the die 2. There are noprotruding ends of the roller. The roller and holder can be dimensionedto stay within the ends of the tool. The work piece contact surfaceprovided by the roller is similar to that of a conventional power presstool. FIG. 10B shows another embodiment of work piece and die 2 where asecond embodiment of roller assembly 7 is in place.

If the roller 11 becomes worn over time it can be readily replacedwithout having to replace the punch 3 and/or die 2 as a whole, or eventhe roller assembly 7 as a whole, or to do substantial work on the punchand/or die 2 to recover its shape. For example, if necessary, the wholeroller assembly 7 can be replaced without having to replace the punchand/or die 2 in its entirety. Alternatively, the holder 9 can beretained and just the roller 11 replaced.

Replacing the roller can involve removing the roller assembly 7 from thepunch 3 and/or die 2. Removal of the roller assembly may be effected bysliding the roller assembly out of the cavity in punch 3 and/or die 2.Some force may need to be applied to slide the assembly 7 out of thepunch 3 and/or die 2. Once removed from the punch or die, a new roller11 can be fitted to the roller assembly 7 and the roller assembly 7 slidback into the punch 3 or die 2. In some cases the replacement can beeffected without removing the punch or die from the power press. As theroller assembly 7 can be replaced by punching or sliding the parts outof the punch or die and then sliding new parts into the punch or diethere is little skill involved in replacement. This reduces the cost ofreplacing parts as a skilled toolmaker is not required.

Additionally a punch and/or die can be altered to allow the roller andholder to be retrofitted to the punch or die. Although it is impracticalto tap a threaded screw hole into a hardened steel punch or die, it ispossible to cut a cavity or slot for the roller and holder using a wireerosion machine. Wire erosion machines were developed in the 1960s andcan be used to cut hardened steel tools. A wire erosion machine can beused to cut a cavity in a hardened steel tool—including one damaged inthe shoulder area—to allow a roller assembly to be retrofitted to thetool. The precision available with a wire erosion machine means that thecavity can be cut to produce an interference fit with the rollerassembly. As the roller or combination of roller and holder can bereplaced when they wear, retrofitting holders and rollers provides aclear advantage over replacing the tools themselves. Cavities forrollers assemblies can also be formed when the tool is first created.While cutting a cavity in the punch 3 or die 2 may slightly reduce thestrength of the power press tool, a similar maximum force per squareinch can still be applied. In general, the force required to form thework piece when the roller assembly is in place will be less than theforce required without the roller as the roller reduces the amount offriction created between the work piece 4 and the punch 3 and/or die 2as the work piece is formed.

Referring again to FIG. 3, in some embodiments the punch 3 may havefriction fitted releasable wear resistant inserts 16 at its lowercontact shoulders. These have radius shaped edges to reduce wear fromcontact with the work piece 4. The punch's inserts 16 can be removed andreplaced when worn, without having to replace the rest of the punch. Theinserts 16 can be made from hardened or coated steel meaning that thebody of the punch can be made from less hard, less expensive materialthat does not need to be hardened. The inserts 16 differ from the rollerassemblies 7 in that they do not have a roller 11. However in somealternative embodiments the punch inserts may be formed and function thesame as the die roller assemblies 7. In other embodiments, where wear isnot such an issue, but slippage of a work piece is, the punch inserts 16may be serrated to better grip the work piece when acting on it.

In some aspects of the invention there may be a selection of the rollerassemblies 7 and inserts 16, each made of different materials, or withwork piece contacting parts made of different material, for differentjobs.

Referring to FIG. 11, an alternative embodiment of the invention mayhave solid one-piece inserts 17—i.e. without a roller 11. These can beformed of materials of different characteristics, e.g. co-efficient offriction, depending on the needs of a particular job, and can be readilyreplaced when worn.

FIGS. 13 and 14 illustrate a roller assembly for a die or punchaccording to a further embodiment. In this case the roller 18 isretained in the cradle 19 of the holder 20 without the use of horseshoeshaped clips. Rather, the roller 18 is retained by way of retainingplates 21 screw fastened at each end of the cradle 19. Stubs 22 at eachend of the roller 18 engage and are held in apertures 23 of theretaining plates 21 respectively. This form of attachment of the rolleris particularly useful where the included angle of the shoulder of thepunch or die to which the roller assembly is to be fitted is less thanapproximately 70 degrees and in which circumstances the holder enclosesless than 180 degrees of the roller and so does not hold it in placevertically. In the embodiment shown in FIGS. 13 and 14 the retainingplates provide the means for connecting the roller and holder to preventthe roller moving both vertically and along its rotational axis withrespect to the holder. Another advantage of using retaining plates inthe way shown is that the retaining plates only hold the roller to theholder. They do not fix the roller with respect to the body of the punchor die, meaning that no threaded hole has to be tapped in the punch ordie. As previously described it is not economical to tap a threaded holeinto a hardened steel punch or die. As the retaining plates are attachedto the holder this problem is overcome.

Referring to FIG. 15, in some embodiments the press tool may utilise apunch 23 which moves against a work piece 24 set on a die 25 which iswithout a cavity. The punch 23 has a removable roller assembly 26, whichin turn has a removable roller as described for the other embodiments.FIGS. 16 and 17 show the punch 23 at progressively advanced stages ofoperation when used for shaping the work piece 24.

FIG. 18 shows an embodiment of tool where the die 2 and punch 3 are eachprovided with roller assemblies in their shoulders. The provision of themultiple roller assemblies means that friction experienced on theshoulders of the die 2 and punch 3 during the forming operation issignificantly less than if conventional static die and punch shoulderswere used. The rollers also reduce marking on the work piece beingformed.

While some preferred forms of the invention have been described by wayof example it should be appreciated that modifications and improvementscan occur without departing from the scope of the appended claims.

1-21. (canceled)
 22. A die or punch for a press tool comprising: a body;and a roller assembly having a holder and a roller; the holder shaped toslidably engage with a complementary cavity in the body to facilitatesecure installation of the holder in the body, the holder being able tobe removably inserted into the body to present the roller as a formingedge to shape a work piece in a press tool, the roller being able toturn with respect to the holder when shaping the work piece to protectthe roller against wear.
 23. A die or punch for a press tool accordingto claim 22, wherein the roller comprises a cylinder arranged to turn,and which is replaceable, with respect to the holder.
 24. A die or punchfor a press tool according to claim 23, wherein the roller is releasablysecured to the holder by way of a clip.
 25. A die or punch for a presstool according to claim 23, wherein the roller has a groove tofacilitate securement by the clip.
 26. A die or punch for a press toolaccording to claim 23, wherein the holder comprises a slot to facilitatesecurement of the clip.
 27. A die or punch for a press tool according toclaim 23, wherein the clip is generally in a horseshoe shape.
 28. A dieor punch for a press tool according to claim 22, wherein ends of theroller are held in end retaining plates and the roller is able to rotatewith respect to the plates.
 29. A die or punch for a press toolaccording to claim 22, wherein the holder has at least one channeladapted to enable the passage of lubricant from an aperture in theholder to the roller.
 30. A die or punch for a press tool according toclaim 29, wherein there are two of the channels which run from oppositeends of the holder.
 31. A die or punch for a press tool according toclaim 30, wherein the holder has at least one fastening groove in a sidethereof adapted to engage with a complementary protrusion in the body tofacilitate secure installation of the holder in the body.
 32. A die orpunch for a press tool according to claim 31, wherein there are two ofthe fastening grooves, each running substantially the length of oppositesides of the holder.
 33. A die or punch for a press tool according toclaim 22, wherein the holder is shaped to retain the roller in place inthe press tool.
 34. A die or punch for a press tool according to claim22, wherein the roller assembly is at an angle with respect to the body.35. A die or punch for a press tool according to claim 22, wherein thepress tool is fitted to a power press.
 36. A die or punch for a presstool according to claim 22, wherein the press tool is formed fromhardened steel.
 37. A die or punch for a press tool according to claim22, wherein the roller assembly is retrofitted to the die or punch. 38.A die or punch for a press tool according to claim 22, wherein theholder has a wider portion at or towards the base of the holder whencompared to the roller end of the holder.